In conventional small-sized motors such as the one disclosed in United States Patent of Yukasada et al, U.S. Pat. No. 3,662,240, issued May 9, 1972, a centrifugal governor switch is disposed on a rotor core or on the opposite side of the commutator with respect to the rotor. One example of such conventional small-sized motor is elucidated referring to FIG. 5 to FIG. 10 hereof. FIG. 5 is a sectional elevation view of a small-sized motor wherein a rotor 3 is mounted on a shaft 5 and a ring-shaped stator magnet 7 is installed in a metal case 6. On both (upper and lower) sides of the rotor 3, a centrifugal governor switch 1 and a commutator 4 are mounted on the shaft 5, with the rotor 3 axially between them.
The centrifugal governor switch 1 comprises, as shown in the plan view of FIG. 6 and in the partly cut-away elevation view of FIG. 7, a molding 9 of an insulating plastic resin, mounted on the shaft 5. A fixed contact plate 8a, having a fixed contact point 11a mounted in an adjustable manner is secured by one end thereof to the molding 9. A centrifugal moving contact plate 8b of resilient metal, having a moving contact point 11b and a centrifugal weight 10 is secured by one end thereof to the molding 9, and a counter weight member 12, 8c is secured to the molding 9.
The commutator 4 comprises, as shown in the plan view of FIG. 8, in the partly cut-away elevation view of FIG. 9 and in the circuit diagram of FIG. 10, a molding 14 of an insulating plastic resin mounted on the shaft 5 and a specified number of metallic commutator segments 13a, 13b, 13c and 13d having risers 131a, 131b, 131c and 131d, respectively. The base parts of the risers 131a, 131b, 131c and 131d, and the one ends, as well as the central inside space among the metallic segment metals 13a, 13b, 13c and 13d are filled and enclosed with the material of the molding 14, so as to be firmly secured thereto. Ends of the coils 2, 2 of the rotor 1 are connected to the risers 131a, 131b, 131c and 131d of the segment metals 13a, 13b, 13c and 13d. Actually, these segment metals 13a, 13 b, 13c and 13d are made of a metal pipe having risers 131a, 131b, 131c and 131d at one end. After molding, when the resin has hardened about the filled and enclosed parts, a specified number of slits, parallel to the axis of the pipe are cut into the pipe wall and the resin within the pipe, thereby electrically isolating the metal pipe into the cylindrically arranged, arcuate metal segments.
Since the commutator 4 and the governor switch 1 are disposed on both sides of (i.e. above and below) the rotor 3, the conventional small-sized motor has the following shortcomings:
Firstly, since the stator magent 17 is disposed in the central part of the inside space in the case 6, the governor switch 1 must be smaller in diameter than the inside diameter of the stator magnet 7, in order that the governor switch 1 can be inserted in the inner-most part of the case 6 through the space centrally of the stator magnet 7. Because of the above-mentioned restriction of the diameter of the governor switch 1, a sufficient centrifugal force is not obtainable and hence a large contact pressure is not obtainable for the contacts 11a and 11b.
Secondly, since the governor switch 1 and the commutator 4 are disposed separately on both sides of the rotor 3, two steps of press-mounting are necessary for mounting the governor switch 1 and the commutator 4 on the shaft 5.
Thirdly, since the governor switch 1 and the commutator 4 are disposed on opposite sides of the rotor 3, long connecting wires are necessary from the fixed contact plate 8a and moving contact plate 8b to the risers 131a and 131d, respectively, besides connections of ends of the coils 2 and 2 to the risers 131a, 131b, 131c and 131d, thereby necessitating soldering of many wire ends.